There are a number of medical conditions for which it has been found that an effective therapy involves driving current through a section of the tissue of a patient. Often, the current is driven between the electrodes of an electrode array implanted in the patient. Generally, the electrode array includes a non-conductive carrier on which typically two or more electrodes are disposed. Once the electrode array is implanted, current is driven from at least one of the electrodes, through the adjacent tissue, to at least one of the other electrodes. The current flow through the tissue influences the tissue to accomplish a desired therapeutic result. For example, an electrode array positioned adjacent the heart may flow currents to stimulate the appropriate contraction and expansion of the heart muscles. There is an increasing interest in implanting electrode arrays adjacent neural tissue so that the resultant current flow induces a desired neurological or physical effect. In one known application, the current driven between the electrodes of an array placed on top of the dura in the vertebral column reduces the extent to which chronic pain signals are perceived by the brain. Alternatively, the array may be placed in a location where the current flow stimulates a feeling of stomach fullness as part of an appetite suppression/weight management therapy. In another application, the current is flowed to tissue or nerves associated with the bladder or the anal sphincter to assist in control of incontinence. Electrodes may be implanted in a paralysis victim to provide muscle control and/or a sense of feeling.
The Applicants' Patent Application No. No. PCT/US2009/33769, FOLDABLE, IMPLANTABLE ELECTRODE ARRAY ASSEMBLY AND TOOL FOR IMPLANTING SAME, filed 11 Feb. 2009, published as WO 2009/111142, the contents of which are explicitly incorporated herein by reference, describes an electrode array that includes a frame on which plural electrodes are arranged in a row by column matrix. An advantage of this electrode array is that it allows current to be flowed between numerous different combinations of electrodes. Depending on which electrodes are operated to function as current sources and sinks, this array can be operated so that there are two or more current flows occurring simultaneously between different sets of electrodes. Once this array is deployed, the practitioner drives current between different combinations of electrodes. Current therefore flows through different sections of tissue. This allows the practitioner to determine between which electrodes, through which tissue, the current flow offers the greatest benefit and/or tolerable side effects. Once the optimal current flow path between the electrodes is determined, the array and its associated power supply are set to operate in this state. Should the electrodes shift or the clinical needs change, the array can be reset to accommodate these changes.
In comparison to other electrode arrays with lesser numbers of electrodes, the above-described array makes it possible to flow current through more sections of tissue and to selectively focus/diffuse the current flow. In contrast to an electrode array with a smaller number of electrodes, use of the above-described array increases the likelihood that the current flow can be set to provide desired therapeutic effects, with tolerable side effects.
Previously, there was a disadvantage of providing an electrode array with numerous individual electrodes that collectively occupy a large surface area. Specifically, owing to the size of these arrays, it was believed that the only way to position them against the tissue through which current is to be driven was to cut a relatively large incision in the patient to provide access to the target tissue. Typically, this incision is more than 3 cm in length and, often at least 5 cm in length. Once the incision is made, it is then usually necessary to retract at least a portion of the tissue overlying the target tissue. In some insertion procedures, removal of some of the overlying tissue is required. The electrode array was passed through the incision and placed against the target tissue. Once the electrode array was positioned, the incision was closed.
The electrode array of the incorporated by reference WO 2009/111142, is designed in part to be implanted in a patient without requiring such a large sized incision, tissue removal and the attendant trauma that results from these procedures. The Applicants' array of this incorporated-by-reference document is designed so that the electrodes are disposed on a frame formed from a superelastic material. A superelastic material is one that, after being subjected to appreciable bending or folding, returns to its initial state. Once this electrode array is formed, the assembly is then folded or rolled into a form that has a side-to-side width appreciably less than its width in the unfolded/unrolled state.
It has been proposed that this folded/rolled array then be placed in a deployment cannula. This electrode array-deployment cannula assembly is then fitted into a slightly wider insertion cannula. Once a portal, a puncture opening, is formed in the patient, the cannulae and electrode array are directed toward the surface of the tissue in the body against which the electrode array is to be deployed. The deployment cannula, with folded/rolled electrode array contained therein, is positioned over the target tissue. The deployment cannula is then retracted back into the insertion cannula while the electrode array is blocked from such movement. The retraction of the deployment cannula uncovers the folded/rolled electrode array. As a consequence of the electrode array being formed on the frame of superelastic material, the array, upon being uncovered, unfolds/unrolls back to its initial shape. The unfolded/unrolled array extends over the target tissue, the tissue through which it is believed current flow will provide the desired therapeutic effect.
A benefit of the above assembly is that only a relatively small portal is formed in the patient in order to position the cannulae-containing assembly in the vicinity of the target tissue. The need to form a large incision and possibly remove tissue in order to position the assembly, and the attendant trauma associated with such an incision is eliminated. It should similarly be appreciated that another advantage of avoiding having to make such a large incision in the patient is that it lessens the degree to which the internal tissue of the patient is exposed to the ambient environment and infection-causing agents in the environment. Thus, it should be appreciated that not having to make a large incision in a patient can reduce the patient's recovery time and risk of complications.
Likewise, the above procedure can typically be performed in less time than it takes to implant the electrode array through an open incision. This is consistent with one of the goals of modern surgical practice; minimizing the time the patient is held under anesthesia.
The above-described assembly and method for percutaneously deploying an electrode array eliminates having to form a large incision into the patient and the disadvantages associated with having to make such an incision. However, one limitation associated with this assembly and method is that it works best if the insertion cannula is positioned a relatively short distance from the target location over which the electrode array is to be deployed. Sometimes anatomic features or safety concerns makes it difficult, if not impossible, to place the cannulae at a location so that, upon deployment, the array seats over the target tissue. In these situations, ideally, it should be possible to advance the deployment cannula relative to the insertion cannula so the array is positioned over the target tissue. However, intervening tissue may block the advancement of the deployment cannula and array to the target tissue. This can make it difficult, if not impossible, to use the delivery assembly to deploy the electrode array.